add filter to update_option to allow modifications to option prior to saving

Description

At present, Its impossible to filter an option being updated, While there is an action which can be hooked to notify the option has changed, it cannot be modified directly.

Attached is a patch which adds 'pre_update_option_<option_name>', It can be used in combination with a filter on get_option() to seemingly hide various portions of options to the rest of the WordPress admin (or theme, etc), and then add them back in if the option is modified.